This invention relates to an electron beam scanning device including an electron probe microanalyzer, a scanning electron microscope and an electron beam exposure system where the device is capable of producing the electron beam spot on a specimen or target and also adjusting the electron beam current on the specimen or target by means of a converging lens system.
In electron probe microanalyzers and scanning electron microscopes, it is necessary to vary the electron beam accelerating voltage and the current value of the electron beam irradiating a specimen, within very wide ranges, namely 100 V.about.several tens KV and 10.sup.-12 A.about.10.sup.-6 A, respectively. Further, it is also necessary to vary the working distance, namely the distance between the specimen surface and the lower pole piece of the objective lens (i.e. final stage condenser lens) within the wide range, and to stepwise change the aperture diameter of the aperture means for controlling the angle of the cone of electron beams in the converged spot on the specimen surface.
An operator usually controls the above accelerating voltage (Ve), electron beam current (Ie), working distance (Wd) and aperture diameter (Da) manually according to the specimen kind, whether it is an organism, metal, semiconductor, ceramic or some other specimen, and the surface condition of the specimen so that a high signal-to-noise ratio in the video signal and a high resolution scanning electron image are obtained. The accelerating voltage (Ve) and working distance (Wd) among the above four controllable factors are determined readily by comparison based only on the specimen kind and the surface condition of the specimen. However, it is difficult to optimally select the aperture diameter (Da) for producing the minimum diameter of the electron beam spot on the specimen surface under the condition of the desired beam current (Ie) and the selected values of the other two factors. Usually, this selection is based upon the operator's prior trial and error experience. This selection is a troublesome and time consuming operation.